1. Field of the Invention
Aspects of the present invention relate generally to writing data to, and reading data from, recording media, and more particularly to a system and method of laser bias level control.
2. Description of Related Art
Recently, rewritable (RW) optical recording media have gained popularity. Compact disc (CD), digital versatile disc (DVD), high density DVD (HD DVD), and blu-ray disc technologies have been evolving to allow multiple write operations in accordance with several standards. For example, both −RW and +RW technologies enable a disc drive head to write data to a disc multiple times without first erasing the entire disc.
In accordance with these and other optical data recording technologies, a disc drive head generally comprises a laser or other optical source and an optical pickup unit to detect lased or other collimated light reflected off the disc during read operations. As is generally known with respect to RW media applications employing such a laser, it may be desirable in many instances to control the bias level of the laser very accurately, though this has heretofore not be practically possible given current technologies. Even a small deviation in bias level may result in a slightly inaccurate ratio of erase power to write power, i.e., the Pe/Pw ratio (or Epsilon, ε, ratio), which can have deleterious effects on the efficiency with which data are written, the usable life of the recording media, or both.
In many instances (such as, for example, during +RW write operations), there is no way of sampling the bias level accurately, so indirect methods of estimating the bias level must be used. Some approaches do not even attempt to control the bias level, but rather rely upon an inefficient technique of regularly or periodically interrupting a write process and resetting the bias level to a desired or appropriate value during a read process before resuming the write. Such systems sacrifice transfer speed (i.e., data throughput rate) because they include no accommodation for managing bias level; in order to achieve optimal transfer speeds, it is generally desirable to avoid interrupting the write process, and accordingly, it may be beneficial to control the bias level continuously.
Therefore, it may be desirable in some instances to provide a system and method that can accurately control the bias level of a laser in optical recording media applications using reliable and readily available data.